That old chestnut ain't going to work. Not when both candidates are set square against your core values.
If Rudy won the Republican nomination after a fair primary fight and social conservatives refused to support him, voting for a third-party candidate and leading to a Hillary Clinton victory, social conservatives will be responsible for Hillary's election.
The issue of abortion will not be decided at the executive level of government, and neither the House nor the Senate has the political will to pass a constitutional amendment outlawing it or overturning Roe. The issue will be decided in the courts.
Social conservatives had better pray Hillary is never elected President and should work to prevent such an abomination at all costs, even if it means the election of a Republican moderate. Her nominess to the bench will make Steve Bryer look like Antonin Scalia. With Rudy you at least get a shot at constructionists.
Of course, if you don't give a rat's ass about the unborn, vote for a third-party candidate in a Hillary/Rudy election should the opportunity arise.